Cameras based on onsemi image sensors record descent of Perseverance rover to Mars

‘Seven minutes of terror’ was NASA’s description of the most challenging phase of the Mars Perseverance Rover’s mission: the entry, descent, and landing (EDL). In these intense seven minutes, the spacecraft enters the Martian atmosphere at 12,500 miles per hour and decelerates to zero for touch-down. Perseverance completes this phase autonomously: its radio signal declaring whether it has succeeded takes longer, some 11 minutes 22 seconds, to reach the Earth.

The Mars Perseverance Rover includes a total of 23 cameras used in the engineering, EDL, and science camera systems. NASA intended the EDL camera systems to capture EDL events in more detail than in previous missions. The camera system took full-color video during the vehicle’s descent through Mars’ atmosphere to the surface. The images captured on the way down help Perseverance’s mission planners to select the rover’s first ventures on the planet. 

The EDL camera system itself consists of seven cameras: 

• Parachute uplook cameras
• Descent-stage downlook camera
• Rover uplook camera 
• Rover downlook camera
• Landing camera (LCAM)

The function of the LCAM was to provide critical image data to the lander vision system (LVS) required for navigation: an onboard computer analyzed the images to compare them with a map so that Perseverance could autonomously choose the safest landing site relative to its position during the descent. It also monitored the deployment of the parachute during the parachute descent phase of EDL.

NASA’s design challenge
The challenge for the developers of the Mars mission’s EDL and LCAM camera systems was to improve knowledge of EDL and LVS system performance by using a video imaging system to capture key EDL events, including parachute deployment, sky crane deployment, rover touchdown, and lander rocket plume dynamics. Image capture would also help autonomous terrain-relative navigation. 

The process for selecting camera technology involved qualification of commercial off-the-shelf hardware, with particular focus on evaluating its cost and ease of system integration.

Fig. 1: Image acquired during Perseverance’s descent to Mars, using its parachute up-look camera A. (Image Credit: NASA and JPL-Caltech)

A vital requirement of the EDL camera system was that it should not interfere with the flight system during EDL. The camera system design could also not require changes to the flight hardware or software systems inherited from the Mars Science Library Curiosity rover. 

The camera systems’ minimum frame rate requirements were 30 frames/s to capture images of the parachute. The three parachute uplook cameras were to start capturing images at a frame rate of 75 frames/s prior to parachute deployment, and to drop the frame rate to 30 frames/s after 30 s until the backshell separation about 98 s later. 

Each parachute uplook camera was expected to take approximately 5,190 images, a total of 15,750 for the system. The rover downlook camera system was to start capturing images just before heatshield separation, continuing through to touchdown on the surface of Mars. This camera system captured images at 30 frames/s for approximately 260 s for a total of around 7,800 images. 

The rover uplook camera system was to start capturing images just before the rover separated from the descent stage, continuing through to rover touchdown on the surface of Mars. The rover uplook camera captured data at 30 frames/s for approximately 140 s, capturing around 4,200 images.

Landing camera
The landing camera requirements include a field of view of 90° by 90°, an array resolution of 1,024 px x 1,024 px, and a global shutter sensor. The camera system solution also needed to have a frame latency of less than 100 ms between the camera image trigger and the last pixel output of the image, a frame rate of up to 2 Hz, and a signal-to-noise ratio of greater than 80:1 with a 1 ms exposure time under the illumination conditions of the Mars environment.

The solution
The Perseverance mission teams selected cameras from the FLIR Systems Chameleon®3 family of cameras for the EDL systems. The solution chosen for the parachute uplook camera, rover uplook camera, rover downlook camera and landing camera systems includes sensors from the onsemi PYTHON family of CMOS image sensors. 

The EDL engineers chose the PYTHON-based cameras from FLIR because of their global shutter operation, small optical format, versatility, and read-out speed: full frame rate, and quadratic speed increase reading out smaller regions of interest. Within the Chameleon3 product family, the PYTHON-based cameras offered the highest frame rates. The correlated double sampling (CDS) support in global shutter mode reduces noise to single digits, and offers increased dynamic range to retain image detail in high-contrast environments. 

The parachute uplook camera, rover uplook camera, rover downlook camera systems use PYTHON 1300 image sensors. The landing camera uses a monochrome PYTHON 5000 global shutter CMOS image sensor with a pixel array of 2592 px by 2048 px, and on-chip 8- or 10-bit digitization at up to 100 frames/s. 

Result
The next-generation imaging system of the Perseverance rover improved the operational capabilities of the Mars 2020 mission by providing the first-ever color video of touchdown on the Martian surface. The video footage of crucial entry, descent, and landing events successfully documented the mission systems’ performance. It will serve to instruct the design for EDL systems in the future. 

Likewise, the success of the landing camera in capturing Martian surface images to assist terrain-relative navigation will facilitate more targeted landing capabilities for future missions to Mars. More than 1,300 images and video captured by these camera systems are available for viewing on the Mars 2020 mission Perseverance Rover website.